As a method for reducing carbon dioxide, one of the causes of global warming, the conversion from fossil resources to biomass resources is desired. Specifically, investigations have been carried out to use ethylene (1) obtained from methanol produced by a high-temperature gasification of biomass resources, or ethylene (2) obtained from ethanol produced by ferment of biomass resource by a dehydration reaction, as a substitute of ethylene produced by a naphtha cracker.
On the other hand, another important basic raw material for petrochemicals obtained from a naphtha cracker is propylene, and in order to produce propylene directly from methanol or ethanol, a conversion by a certain kind of chemical reaction is usually necessary. Here, a metathesis reaction, in which the same or different kinds of olefins are reacted to give an olefin having a different structure from those of the original ones, is generally very effective because ethylene is converted to propylene by reacting with 2-butene.
However, in general, a catalyst used in a metathesis reaction is extremely sensitive to water, an oxygen-containing compound and a nitrogen-containing compound, and thus deterioration of catalyst activity is developed immediately after a raw material containing these impurities is used. For example, a tungsten oxide catalyst which is a typical metathesis catalyst when used in a fixed bed reaction as disclosed in U.S. Pat. No. 4,575,575 (Patent Document 1) and in the Journal of Molecular Catalysis, Volume 28, page 117 (1985) (Non-Patent Document 1), is poisoned to a large extent by water present in raw materials. Therefore, it is considered necessary to purify butene of all the raw materials using an alumina as an adsorbent.
Ethylene, which is another raw material, is usually produced by a naphtha cracker. More specifically, nitrogen- and sulfur-containing impurities are removed from raw material naphtha and then the raw material is introduced into a naphtha cracker, and a high-temperature cracked gas obtained from the naphtha cracker is immediately cooled, alkali-washed, and purified by adsorption, and then separated into each component by respective distillation towers. Accordingly, the ethylene obtained from a naphtha cracker is not necessarily to be purified by adsorption when used in a metathesis reaction.
However, ethanol obtained from biomass resources, contains not only water but also a carbonyl compound that is an impurity from a fermentation process and a nitrogen-containing compound that is a decomposition product or a contaminant of an enzyme, and ethylene is contaminated by these compounds themselves or their decomposition products while obtaining the ethylene by a dehydration reaction, whereby the activity of a metathesis catalyst is adversely affected. Accordingly, development of a method for purifying the ethanol has been desired.    Patent Document 1: U.S. Pat. No. 4,575,575    Non-Patent Document 1: Journal of Molecular Catalysis, Volume 28, page 117 (1985)